The present invention pertains to engine control systems and in particular to input sensor circuits which are especially useful in electronic engine control systems of the digital type.
The application of electronic controls to engine control systems accomplishes substantial improvements in engine performance. With the use of electronics a large number of inputs may be sensed, and the information obtained therefrom utilized to provide precise control of selected events associated with operation of the engine. An outstanding example is the Chrysler Electronic Lean Burn Engine which monitors, via input sensors, various engine operating conditions to precisely control the timing of spark ignition. This remarkable engine achieves reduced exhaust emissions and improved fuel economy without the use of other devices (such as catalytic converters, exhaust gas recirculation) which had heretofore been required on internal combustion engines to meet Federal emission standards and which lowered fuel economy. The Chrysler Electronic Lean Burn Engine, as currently manufactured and sold by Chrysler Corporation, utilizes several analog sensors and analog circuits for converting the sensor information into analog electrical signals utilized in controlling spark timing.
The desirability of incorporating a digital microprocessor in an electronic engine control system has heretofore been recognized. While engine control systems utilizing digital microprocessors are known in the art, a serious impediment to their commercial feasibility is that suitable input sensors are not available. Although in some instances there do exist digital sensors which can provide digital inputs to a microprocessor, these digital sensors are generally very expensive. Less expensive digital sensors do not possess the requisite accuracy and ruggedness which are necessary for use in an engine control system. Analog sensors can be used in certain instances but these require complicated analog-to-digital converter circuits. Thus, while digital microprocessor technology has developed to a point where microprocessors are suited for engine control application, the technology relating to input sensors for these microprocessors has not kept pace.
The present invention is directed toward input sensor circuits for a digital microprocessor which do not require digital sensors, but rather utilize existing analog sensors. However, input information is provided in a digital form which may be directly acted upon by the microprocessor. With the present invention, input sensor parameters representative of selected inputs are converted into binary words. By way of example, conventional resistive, capacitive, inductive, or voltage type sensors may be used and the parameters thereof converted into corresponding binary words which may be acted upon directly by the microprocessor in its calculations for the particular engine control function which is being accomplished. Moreover, the invention is susceptible to compact packaging and can be readily calibrated for compatibility with the particular range of values of the input sensor parameters. Indeed, the invention can be incorporated, to a substantial extent, in its own integrated circuit, thereby promoting reliability and minimizing costs. The speed at which information is obtained is so fast that a number of sensors can be monitored by means of a multiplexing technique so that the amount of circuitry required is kept to a minimum. With the present invention a serious obstacle to the adoption of digital microprocessors for engine control application is removed.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which are to be considered in conjunction with the accompanying drawings which illustrate a preferred embodiment of the invention according to the best mode presently contemplated in carrying out the invention.